Extracorporeal membrane oxygenation (“ECMO”) is a form of cardio-pulmonary bypass that is employed to support critically ill patients with acute cardiac failure, respiratory failure, or combined cardiopulmonary failure. A typical ECMO circuit 100 as shown in FIG. 1 consists of multiple components including cannulas, tubing, an oxygenator, and pump with a controller. A heater-cooler element may be added for temperature management as well. Generally, a venous cannula 2 is inserted either into a large vein, such as a femoral vein, or the right atrium of the heart for drainage of blood from the patient. The blood is carried via bypass tubing 3a to a pump (not shown), which provides forward flow through the circuit, and to an oxygenator (not shown), which both oxygenates the blood and allows removal of carbon dioxide. The blood is then returned to the patient via bypass tubing 3b connected to a return or arterial cannula 4, which is generally placed in either the aorta or a large peripheral vessel, such as the femoral artery. Depending on the configuration, an ECMO circuit can provide gas exchange for patients with acute pulmonary failure, or both gas exchange and hemodynamic support for patients with acute cardiac or combined cardiopulmonary failure. In the setting of acute cardiac and pulmonary failure, ECMO can provide immediate restoration of perfusion and oxygen delivery to tissues, thereby preventing worsening acidosis, shock, multisystem organ failure and ultimately death and allowing for time for either organ recovery or diagnosis and intervention.
Use of this form of temporary mechanical circulatory support was initially reported in 1972. Since its introduction, technological advances in all components of the ECMO circuit have occurred. For example, improved cannula design has allowed more facile insertion with less trauma to blood vessels. Advances in pump and oxygenator design have allowed for greater efficiency and less trauma to blood elements. In the context of these advances, it was discovered that ECMO could serve as a valuable tool in supporting critically ill patients afflicted with H1N1 influenza. In its most severe manifestations, H1N1 was associated with a high mortality rate and it was found that ECMO could reduce mortality in these critically ill patients. Improvements in ECMO technology, along with its demonstrated success with critically ill H1N1 patients, have led to a dramatic growth in the use of ECMO for patients with acute cardiopulmonary failure.
ECMO is generally considered to be a supportive technology intended to provide oxygen and hemodynamic support to patients with acute cardio-pulmonary failure through a closed system. Many patients that require ECMO also require invasive procedures for diagnosis and potentially intervention. Many of these procedures, such as left and right heart catheterization, percutaneous coronary intervention, or insertion of catheters for instillation of thrombolytics, require access to the cardiovascular system, which is usually established by inserting an introducer sheath into a peripheral vessel after obtaining access with a needle. However, institution of ECMO generally requires thorough systemic anticoagulation to increase blood flow and prevent clotting. Anticoagulation, however, complicates obtaining access to the vascular system for other subsequent diagnostic and therapeutic procedures, as the anticoagulants cause an increased risk of bleeding when attempting to access a vessel. Furthermore, vascular access is often obtained in the clinical setting by palpating a patient's pulse as a landmark for locating the blood vessel. ECMO provides laminar flow and a patient on ECMO may have very little or no difference in systolic or diastolic blood pressure, resulting in a very low pulse pressure. While a patient may have adequate blood pressure, there may be very little pulsatility and it may be difficult or impossible to palpate a pulse while on ECMO. Thus, despite the potential necessity for vascular access for subsequent diagnostic and therapeutic procedures while on ECMO, obtaining vascular access in patients on ECMO may be challenging and result in complications including vascular injury and bleeding.
Since establishment of an ECMO circuit requires insertion of cannulas into the vascular system, the ECMO circuit itself has the potential to serve as an access point to the cardiovascular system and allow the performance of diagnostic and therapeutic procedures to promote the recovery of the patient. Utilizing the ECMO circuit itself for access to the cardiovascular system would circumvent the challenges and risks associated with attempting to access another blood vessel. However, an ECMO circuit is generally not used as a vascular access point in clinical practice as a safe and facile means of doing so does not exist with currently available technology.
For example, the arterial or in-flow cannula 4 generally represents the most proximate component of the ECMO circuit to the patient's cardiovascular system. This arterial cannula 4 is typically inserted into a large peripheral vessel, such as the femoral or axillary artery, or directly into the aorta. Most commercially produced cannulas have a small, perpendicular side port 5 with a Luer connector, as shown in FIG. 1. This side port 5 allows air to be eliminated from the circuit and also allows for establishment of a secondary circuit, such as for perfusion of blood to the ipsilateral limb. Such secondary circuits are established by a secondary circuit connector 13 attaching to the side port 5 of the arterial cannula. Secondary circuit tubing 14 directs blood from the side port 5 to a superficial cannula 10, such as a superficial femoral arterial cannula. Both the main arterial cannula 4 and the superficial cannula 10 may be introduced into the artery at the same insertion point 12, with the cannula 4 being directed toward the heart, and the superficial cannula 10 being directed toward the ipsilateral limb, such as the leg in a femoral arterial setting. The secondary circuit therefore allows perfusion into the ipsilateral leg and prevents ischemia and tissue damage in the leg.
Many patients on ECMO systems will typically require diagnostics and therapeutic interventions, which are commonly facilitated by the placement of an introducer sheath 15, shown in FIG. 2, in the patient's artery. The introducer sheath 15 may also include a hub 16 with side arm 16a for venting air out of the system through venting tubing 17 by operation of a valve 18. The side port 5 of an ECMO arterial cannula 4 represents a potential access point to the ECMO circuit for vascular access. However, current vascular introducer sheaths 15 have no mechanism of interfacing with the side port 5. As is evident from FIG. 2, arterial sheaths 15 are too long and incompatible with the short right angle side port 5 provided in a cannula 4. They therefore offer no mechanism to negotiate the right angle presented by the side port 5, and no mechanism to direct a diagnostic or interventional wire or catheter in the appropriate direction (toward the patient rather than toward the ECMO pump) once inserted. Because insertion is not possible, introducer sheaths 15 provide no mechanism for establishing a hemostatic seal to the cannula 4, which would be needed for safe insertion of a wire or catheter. Attempts to insert a standard arterial sheath 15 into the side port 5 of a cannula 4 would result in uncontrolled bleeding around the sheath 15, inability to maintain the sheath 15 in appropriate position, kinking of the sheath 15, misdirection of intervention devices such as wires or catheters, and inability to pass wires or catheters altogether. For these reasons, currently available arterial sheaths are not amenable for insertion directly into a cannula.